This invention relates to door latching means, and, more particularly, to a latch-bolt assembly, having a fusibly-actuated deadlocking for use, especially, in a fire-rated door.
To reduce the likelihood that fire will increase and/or spread, it is necessary to insure that a closed, fire-rated door remains closed by retaining the latchbolt thereof in its door-latching disposition. In the prior art, fusibly-actuated deadlocking arrangements are known. The known, fusible systems, notwithstanding their acceptable functionings, do have undesirable limitations. One such fire safety door latch is exemplary of prior art systems. In this patented arrangement, it is necessary to have a plate, with a hole formed therein, confronting the innermost portion of the latchbolt, and that portion of the latchbolt must have another hole formed therein, so that a fusible link or plug can be fitted into the two holes. Besides this required machining, for the fusible plug, it would appear that the plug-bearing latchbolt would serve as a heat sink and inordinately delay the fusible release of the plug. Another prior art arrangement discloses a cable connected to a door-knob crank and to a latchbolt, spring-loaded link, with the cable displaced from linearity by a fusible roller. In another fusible arrangement, a fusible pin, set into an inner end of the latchbolt, holds a spring-loaded dowel-like element within a transverse bore in the latchbolt. Upon melting of the pin, the dowel-like element projects from the latchbolt and enters a bore, provided therefor, in the casing of the assembly.
The aforesaid, and similar prior art arrangements, for fusibly deadlocking a latchbolt, are not without merit. However, they are bulky, or complicated, or expensive to manufacture and service, and require extraneous parts and components for the fabrication thereof.
What has long been needed is a fusibly-actuated deadlocking arrangement which is of simple, straightforward construction and, most significantly, warrants no extraneous elements for construction thereof, i.e., a fusibly-actuated deadlocking arrangement, for a latchbolt assembly, which requires no more parts and/or components than a standard, off-the-shelf, non-fusibly deadlocking, latchbolt assembly.
The foregoing illustrates limitations known to exist in present devices and methods. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.